Straddled Band Aligned CuO/BaTiO₃ Heterostructures: Role of Energetics at Nanointerface in Improving Photocatalytic and CO₂ Sensing Performance

This work details novel insights on the role of energetics, that is, energy band bending and built-in potential at the nanointerface of CuO/BaTiO3 forming type I p/n heterostructures, evaluated by correlating X-ray photoelectron spectroscopy and ultraviolet diffuse reflectance spectroscopy studies. Cetyltrimethylammonium bromide (CTAB) assisted hydrothermal route was used to synthesize BaTiO3 cuboids with six active {100} facets, and its CuO based heterostructures were tested for bifunctional applications in environmental nanoremediation. Straddled CuO/BaTiO3 heterostructures reported herein showcased exceptional flexibility as a ultraviolet (UV) active photocatalyst for methyl orange (MO) degradation and chemo-resistive CO2 gas sensor. CuO/BaTiO3 heterostructures in equimole ratio could degrade 99% MO in 50 min with rate constant (κ) of a first-order reaction observed to be 10 and 100-fold greater in comparison with BaTiO3 and CuO samples, respectively. Subsequently, in a parallel application, trials were carried out on CuO/BaTiO3 heterostructures for their sensitivity and stability toward CO2 gas below 5000 ppm. Upon Ag decoration, the sensor response improved compared to CuO/BaTiO3 heterostructures at 160 °C, with enhanced response/recovery times (t90) of 300 and 320 s, respectively towards 100 ppm CO2 gas. Improved photoactivity was rationalized in terms of effective charge severance of photogenerated e–h pairs owing to favorable band alignment, while the optimum CO2 sensor response was attributed to efficient nanointerfaces configured in large numbers and Ag0/Ag+ acting as redox couple.